REV. A

ADM1025/ADM1025A

–13–

USING THE ADM1025/ADM1025A

Power-On RESET

When power is first applied, the ADM1025/ADM1025A per-

forms a “power- on reset” on several of its registers. Registers

whose power-on values are not shown have power-on conditions

that are indeterminate. Value and limit registers are reset to 00h

on power-up. The ADC is inactive. In most applications, usu-

ally the first action after power-on would be to write limits into

the Limit Registers.

Power-on reset clears or initializes the following registers (the

initialized values are shown in Table VI):

– Configuration Register

– Status Registers #1 and #2

– VID0-3 Register

– VID4 Register

– Test Register

INITIALIZATION

Configuration Register Initialization performs a similar, but not

identical, function to power-on reset.

Configuration Register Initialization is accomplished by setting

Bit 7 of the Configuration Register high. This bit automatically

clears after being set.

USING THE CONFIGURATION REGISTER

Control of the ADM1025/ADM1025A is provided through the

configuration register. The Configuration Register is used to

start and stop the ADM1025/ADM1025A, programming the

operating modes of Pins 11 and 16, and provide the initializa-

tion function described above.

Bit 0 of the Configuration Register controls the monitoring loop

of the ADM1025/ADM1025A. Setting Bit 0 low stops the moni-

toring loop and puts the ADM1025/ADM1025A into a low power

mode thereby reducing power consumption. Serial bus commu-

nication is still possible with any register in the ADM1025/

ADM1025A while in low power mode. Setting Bit 0 high starts

the monitoring loop.

Bit 4 of the Configuration Register causes a low going 20 ms (typ)

pulse at the

RST pin (Pin 16) when set. This bit is self-clearing.

Bit 5 of the Configuration Register selects the operating mode of

pin 11 between the default of 12 V analog input (Bit 5 = 0) and

VID4 (Bit 5 = 1).

Bit 7 of the Configuration Register is used to start a Configura-

tion Register Initialization when it is set to 1.

USING THE OFFSET REGISTER

This register contains a two’s complement value that is added

(or subtracted if the number is negative) to either the internal or

external temperature reading. Note that the default value in the

offset register is zero, so zero is always added to the temperature

reading. The offset register is configured for the external tem-

perature channel by default. It may be switched to the internal

channel by setting Bit 0 of the Test Register to 1, setting Bit 6 of

the VID Register to 1, and clearing Bit 7 of the VID Register.

STARTING CONVERSION

The monitoring function of the ADM1025/ADM1025A is started

by writing to the Configuration Register and setting Start (Bit 0),

high. Limit values should be written into the Limit Registers

before starting the ADC to avoid spurious out-of-limit condi-

tions. The time taken to complete the analog measurements

depends on how they are configured, as described elsewhere.

Once the measurements have been completed, the results can be

read from the Value Registers at any time.

REDUCED POWER AND SHUTDOWN MODE

The ADM1025/ADM1025A can be placed in a low power

mode by setting Bit 0 of the Configuration Register to 0. This

disables the internal ADC. Full shutdown mode may then be

achieved by setting Bit 7 of the VID Register to 1 AND Bit 0 of

the Test Register to 1. This turns off power to all analog circuits

and stops the monitoring cycle, if running, but it does not affect

the condition of any of the registers. The device will return to its

previous state when these bits are reset to zero.

5 V OPERATION

nected to any supply voltage between 3.0 V and 5.5 V, but it

should be noted that the device has been optimized for 3.3 V

operation. In particular, the internal voltage divider used to

measure the supply voltage is optimized for 3.3 V. Powering the

25h) to overrange. In this case, the 5 V measurement should be

read from the 5 V Reading Register (Register 23h), instead of

is programmed to read VID4, due to its internal voltage divider,

device is being powered from 3.3 V supply.

REGISTERS

Table V. Address POINTER Register

Bit

Name

R/

W

Description

7–0

Address Pointer

Write

Address of ADM1025/

ADM1025A Registers. See

the tables below for detail.

Table VI. List of Registers

Address

Power On

Register

A7–A0

Value of

Name

in Hex

Registers: <7:0>

Configuration Register

40h

0000 1000

Status Register 1

41h

0000 0000

Status Register 2

42h

0000 0000

VID Register

47h

<7:4> = 0000, <3:0> =

VID3–VID0

VID4 Register

49h

<0> = VID4; Default =

1000 000 (VID4)

Value and Limit

Registers

15–3Dh

Company ID

3Eh

0100 0001

Stepping

3Fh

0010 (Bits 3:0 Version

Number)